This invention relates to a method for improving the properties of fresh meat, especially pork. In particular, this invention relates to the treatment of fresh meat with an aqueous solution of a water-soluble phosphate to prevent PSE condition.
PSE (pale, soft, exudative) condition in meat muscle products, especially pork, is a condition in which the muscle product becomes very pale, stiff, and watery, and loses its water holding capacity. PSE muscle products have been reported to have higher evaporative cooking losses, slower cooking rates, and lower juiciness and tenderness than normal muscle products. Muscle product refers to meat products derived primarily from the animal muscle (bovine, porcine, or seafood), such as bacon and ham.
PSE condition is associated with a rapid rate of postmortem glycolysis, producing a pH below 5.4 while the carcass is still at about 36-40xc2x0 C. The low pH while the muscle temperature is still high causes protein denaturation.
Because most meat products, especially fresh meat products, are purchased based on a visual inspection by the purchaser, abnormal coloration has an adverse effect on the salability of the product. PSE condition produces a tremendous loss in value to pork producers because the loins and hams represent about one-half the market value of the carcass. Over 95 million pigs are slaughtered each year in the United States alone. Estimates put the losses caused by PSE condition at between $50 million to $140 million annually. Reduction or elimination of PSE condition can produce a large economic gain to the meat production and processing industry.
R. G. Kauffman et al., WO 97/46119 and J. Anim. Sci., 76, 3010-3015 (1998), disclose a method for improving the color, water-holding capacity, and organoleptic qualities of meat, especially pork, by injecting or perfusing a solution of sodium bicarbonate into the carcass within 24 hr of slaughter. However, except for the ability of bicarbonates to increase pH, bicarbonates have no known other functional effect on meat proteins. Moreover, excessive alkaline conditions in the meat muscle can contribute to the formation of an undesirable condition known as DFD (dark, firm, dry), as well as contribute to a soapy flavor.
Thus, a need exists for a method for preventing PSE in pork and other muscle products but that does not produce other undesirable effects.
The introduction of water-soluble phosphates, such as orthophosphates, pyrophosphates, and/or polyphosphates with a chain length greater than 2, into muscle products, particularly porcine muscle, prevents the onset of PSE condition as well as the physicochemical changes associated with PSE. The effective materials include not only the phosphates and mixtures of phosphates, but also mixtures of one or more phosphates with the edible salts of various acids, such as citric acid, lactic acid, acetic acid, malic acid, ascorbic acid, gluconic acid, etc., especially their sodium and potassium salts.
A critical parameter is the uniform introduction of the material in the early post-mortem period after slaughter, prior to the onset of rigor mortis in the muscle. A second critical parameter is use of a material that provides an effective acid neutralizing capacity that can be sustained over the effective shelf life of the muscle product. The third critical parameter is use of an optimum ratio of material and concentrations in the muscle product that satisfies the requirements of the second critical parameter while avoiding formation of DFD condition in the muscle product.
Although this invention has application to porcine muscle, it can be used in any other beef, poultry, lamb, or seafood muscle products, such as turkey breast muscle, which are prone to losing its water holding capacity.
An advantage of this invention is that injection of the solution is not limited to PSE-afflicted carcasses, rather the processor can treat all carcasses without fear that normal carcasses will exhibit DFD condition. There are currently no reliable methods or techniques for measuring the presence of PSE in a carcass immediately post-mortem.
Injection or perfusion of an aqueous solution of a material containing one or more water-soluble phosphate salts (xe2x80x9cphosphatexe2x80x9d), such as a orthophosphate, a pyrophosphate, and/or a polyphosphate with a chain length greater than 2, into an animal carcass in the early postmortem period improves the appearance, water-holding capacity and organoleptic quality of the resulting muscle product. In pork, particularly, the treatment greatly inhibits PSE condition.
In practice, immediately after stunning, bleeding and eviscerating of the animal, the carcass is skinned and defatted and the solution injected into the carcass before the onset of rigor mortis. For storage purposes the carcass is then either chilled at 4xc2x0 C. or crust chilled at xe2x88x9215xc2x0 C. until the meat reaches a core temperature of 4xc2x0 C.
For any carcass treated, the aqueous solution has a concentration of about 0.33 to 5% by weight total phosphate salt or salts, preferably about 0.67 to 4.2% by weight, depending on the desired amount of solution and phosphate perfused or injected into the carcass. For example, if it is desired that the carcass contain 0.4% added phosphate and be injected with 12% of its weight with the solution, a solution containing 3.33% phosphate would be prepared. It is preferred that the carcass contain about 0.1 to about 0.5% by weight added phosphate, preferably about 0.3 to about 0.4% by weight added phosphate. Addition of excess phosphate does not further improve the condition of the carcass and may produce an adverse effect, such as DFD condition in the muscle.
Addition of chloride salts enhances protein solubility, thereby acting synergistically with the added phosphates to improve the water holding properties of the muscle fibers in the carcass. Optionally, sodium chloride may be added to the carcass by dissolving it in the aqueous solution and injecting this solution to the carcass. It is preferred that the carcass contain less than 0.5% added sodium chloride, preferably less than or equal to 0.3% sodium chloride. Potassium chloride may be used in place of sodium chloride.
Preferably, the aqueous solution comprises a material that has a pH (1% by wt. aqueous solution) greater than or equal to 6, more preferably greater than or equal to 7, and most preferably greater than or equal to 8. The material may be a single phosphate salt, a mixture of phosphate salts, or a mixture of one or more phosphate salts with one or more non-phosphate compounds.
The choice of material is also dictated by its neutralizing capacity. Neutralizing capacity measured by the number of milliequivalents of base required to change the pH of 100 mL of a 1% by weight solution of the material (i.e. 1 g of material) from about 5 to about pH 7, or by the number milliequivalents of acid required to change the pH of 100 mL of a 1% by weight solution of the material from about 7 to about pH 5. Higher values are more effective in preventing the onset of PSE. Neutralizing capacity values should preferably be at least 2.4, more preferably at least 3 and most preferably at least 4. Preferably the phosphate is a mixture of orthophosphate and polyphosphate (chain length greater than 2), more preferably tetrasodium pyrophosphate and sodium tripolyphosphate with chain lengths of 2 and 3, respectively. This combination provides optimal neutralizing capacity through the use of the orthophosphate and optimal muscle modification through the use of the polyphosphates.
Other ingredients that may be present in the aqueous solution include curing salts (nitrites or nitrates), sweeteners or bulking agents, (sugar, dextrose, corn syrup solids, corn syrup, maltodextrins, etc.), flavoring agents including liquid smoke and spices, and preservatives. The solution may also comprise a salt of an edible acid, such as citric acid, lactic acid, acetic acid, malic acid, ascorbic acid, gluconic acid, etc., especially a sodium and potassium salt.
Injection of the carcass can be accomplished by any number of commercially available injection devices well known to those skilled in the art of meat processing. A typical device includes a pressurized reservoir that holds the aqueous solution connected by a suitable conduit means to a valve-controlled injector head bearing one or more hollow injector needles.
Injection of the solution into a pork carcass must be accomplished before the onset of rigor mortis, preferably within 45 minutes post-mortem and more preferably within 20 to 30 minutes post-mortem. Poultry (for example, chicken and turkey) carcasses undergo rigor much sooner than pork carcasses and therefore must be injected before 20 minutes, preferably 8 to 10 minutes post-mortem. The solution temperature may range from xe2x88x922xc2x0 C. to 40xc2x0 C., preferably below 10xc2x0 C., and more preferably below 4.4xc2x0 C. Preferably the carcass is injected about 10 to 20% of its weight of the solution, more preferably with 10 to 12% of the solution.
Introduction of the solution into intact carcasses on an overhead rail is an advantage, as this minimizes changes to current production methods. This may be achieved by changing the configuration of current brine injection devices that inject the brine at hundreds of points into the muscle. A more uniform distribution of the brine is achieved by using the appropriate injection pressure and tighter needle patterns. Alternatively, injection may be carried by a process similar to current methods by laying the carcass horizontally on a moving conveyor belt and passing it through a manifold of needles. Minor modifications in the injector machine may be required in order to accommodate the size of the carcass.
Alternatively, the solution is perfused into the carcass. In pork, perfusion is preferably performed via the iliac artery. This forces the solution into the pelvic limbs. In poultry, beef, or lamb, the perfusion can be through any major blood vessel that affords perfusion into the majority of meat in the carcass.
The carcass may be tumbled after treatment to afford more nearly uniform distribution of the phosphate solution. Tumbling apparatus is used throughout the meat-processing industry and is well known to those skilled in the art.
In contrast to injection of sodium bicarbonate solutions to prevent PSE condition, (a) phosphates are more stable than sodium bicarbonate in prepared brines; (b) phosphates are already widely used in muscle products, either fresh or precooked, to prevent moisture loss by modifying the properties of the muscle protein; and (c) various phosphates can be mixed to provide the optimum acid neutralizing capacity (buffer capacity) while avoiding formation of a dark firm dry condition in the muscle product.
High Potassium Polyphosphates
Polyphosphates in which the sodium to potassium ratio is 0.5 to 3.8 may be used in addition to, or in place of sodium polyphosphates, especially in applications in which it is desirable to reduce the sodium content of the food, such as in food for individuals who must control their sodium intake.
Preparation of solutions of sodium and potassium polyphosphates by ion exchange is described in Iler, U.S. Pat. No. 2,557,109. Glassy polyphosphate of the following composition:
(K,Na)(n+2)O(PO3)n
in which the ratio of potassium to sodium is about 0.5 to 3.8, preferably 1.0 to 3.8, more preferably 2.4 to 3.6; the average value of n is greater than 9; and at least 85% of the phosphate species comprise more than three phosphate units, may be prepared by the following reaction:
n(MH2PO4)+2MOHxe2x86x92heatM(n+2)O(PO3)n+(n+l)(H2O).
A mixture of monopotassium phosphate, monosodium phosphate, and potassium and/or sodium hydroxide is prepared. The potassium/sodium ratio of the mixture should be the same ratio that is desired in the glassy poly-phosphate product. Preferably, no ions other than sodium, potassium, the ions derived from phosphate (i.e., H2PO4xe2x88x92, HPO4xe2x88x922, PO4xe2x88x923), and optionally, hydroxide, are present. If desired, water may also be added to the mixture.
The (K,Na)/P ratio should be between 1.0 and 1.6 and is adjusted for the desired value of n. The smaller the value of this ratio, i.e. the closer this value is to 1.00, the higher the average value of n.
The mixture is placed in a vessel that can withstand the heating conditions, such as a ceramic or alumina vessel, and heated in an appropriate apparatus, such as a muffle furnace. On an industrial scale, the process may be carried out in a bigger furnace, e.g., 8 feet (about 2.4 M) wide by 15 feet (about 4.6 M) long, lined with zircon ramming mix on the bottom designed to withstand a melt temperature of at least 800xc2x0 C.
The mixture is heated at about 750xc2x0 C. to drive off water and form a clear melt. Heating below 600xc2x0 C. produces materials with insufficient long-chain (n greater than 3) phosphate species. Heating at 780xc2x0 C. produces material that contains excessive insolubles or difficulty-soluble material. Heating should be carried out for about 0.75 to about 1.5 hr. Heating to the required temperature can be carried out in one step or in several stages. After heating, the reaction mixture containing the polyphosphate is, preferably, rapidly cooled so that no crystal growth occurs.
The product is a mixed sodium-potassium polyphosphate glass of formula (K,Na)(n+2)O(PO3)n, in which n and the ratio of potassium to sodium are as discussed above. The polyphosphate glass contains less than 10% by weight water-insoluble material.
The method of this invention can be used to prevent formation of PSE condition. By the early post-mortem injection of a phosphate solution into an animal carcass, the incidence of PSE condition is reduced or eliminated.